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      <title>Synchronized锁的膨胀升级过程 - 交互式测验</title>
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          <div class="quiz-container">
            <div class="quiz-header">
              <h1>Synchronized锁的膨胀升级过程 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
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      <script>
        const quizData = [
  {
    "question": "偏向锁（Biased Locking）的核心设计目的是什么？",
    "options": [
      "在多个线程激烈竞争时，通过操作系统互斥锁保证公平性。",
      "在无竞争或只有一个线程持续访问同步代码块的情况下，减少加锁和解锁的性能开销。",
      "通过自旋等待的方式，避免线程在短时间内被操作系统挂起。",
      "为每个等待的线程创建一个Monitor对象，以便于管理等待队列。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "偏向锁的设计哲学是“乐观”地认为，在大多数情况下，一个锁在被获取后，在接下来的一段时间内只会被同一个线程再次获取。因此，它通过在对象头的Mark Word中记录线程ID来“偏向”该线程，当该线程再次访问时，无需执行任何CAS操作或更重的同步指令，从而极大地降低了开销。",
    "source": "文档中「2. 偏向锁 (Biased Locking)」部分",
    "hint": "思考一下偏向锁的“偏向”二字意味着什么，它适用于什么样的竞争场景？文档中提到“目的是在无竞争的情况下...”。"
  },
  {
    "question": "根据文档，当什么情况发生时，偏向锁会升级为轻量级锁？",
    "options": [
      "当持有偏向锁的线程执行完同步代码块并退出时。",
      "当系统GC（垃圾回收）发生时。",
      "当另一个线程尝试获取已经被某个线程持有的偏向锁时。",
      "当持有偏向锁的线程再次进入同一个同步代码块时。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "偏向锁的“偏向”状态只有在出现竞争时才会被打破。当第二个线程尝试获取这个已经被偏向的锁时，JVM会意识到存在竞争，此时它会撤销偏向锁，并将锁状态升级为轻量级锁，让竞争的线程通过自旋来尝试获取锁。",
    "source": "文档中「3. 轻量级锁 (Lightweight Locking)」部分",
    "hint": "锁的升级通常是由竞争加剧引起的。文档中描述了“如果另一个线程尝试获取...”时会发生什么。"
  },
  {
    "question": "轻量级锁（Lightweight Locking）在尝试获取锁时主要采用哪种技术来避免线程阻塞？",
    "options": [
      "线程上下文切换",
      "CAS（Compare-And-Swap）操作和自旋",
      "操作系统互斥量（Mutex）",
      "记录线程ID到Mark Word"
    ],
    "correctAnswerIndex": 1,
    "explanation": "轻量级锁的核心机制是自旋。当一个线程尝试获取锁时，如果锁已被占用，它不会立即被挂起，而是会执行一个忙等待循环（自旋），并在此期间反复尝试通过CAS操作来获取锁。这种方式适用于锁占用时间很短的场景，可以避免昂贵的线程阻塞和唤醒操作。",
    "source": "文档中「3. 轻量级锁 (Lightweight Locking)」部分",
    "hint": "轻量级锁试图比重量级锁“更轻”，它避免了哪种高开销的操作？文档提到了“采用自旋的方式进行锁竞争”。"
  },
  {
    "question": "在什么情况下，`synchronized` 锁会从轻量级锁膨胀为重量级锁？",
    "options": [
      "当第一个线程首次进入同步代码块时。",
      "当多个线程争抢同一把锁，并且自旋尝试失败或竞争过于激烈时。",
      "当锁对象被序列化时。",
      "当持有锁的线程调用了`wait()`方法时。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "当多个线程竞争轻量级锁，且自旋一定次数后仍然无法获取锁时，JVM认为竞争已经非常激烈，继续自旋会浪费CPU资源。因此，锁会膨胀为重量级锁，将竞争的线程放入等待队列并挂起，交由操作系统来统一调度和唤醒，这涉及到用户态到内核态的转换。",
    "source": "文档中「4. 重量级锁 (Heavyweight Locking)」部分",
    "hint": "重量级锁是应对“激烈”竞争的最后手段。想一想，当自旋也无法解决问题时，系统会怎么做？"
  },
  {
    "question": "关于锁膨胀为重量级锁后的一个重要特性，以下描述哪项是正确的？",
    "options": [
      "重量级锁在竞争减少后，会自动降级为轻量级锁以优化性能。",
      "重量级锁的性能开销比轻量级锁的自旋要小。",
      "一旦锁升级为重量级锁，即使后续没有竞争，它也不会再降级。",
      "重量级锁会将锁的指针指向线程的栈帧。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确指出，锁的升级过程是单向的。一旦锁膨胀为重量级锁，JVM不会再将其降级回轻量级锁或偏向锁状态，即使后来锁的竞争程度降低了。这个特性意味着一次激烈的竞争可能会对这个锁对象未来的性能产生持续影响。",
    "source": "文档中「5. 锁膨胀的影响」部分",
    "hint": "在“锁膨胀的影响”一节中，有一个关于锁状态变化的“不可逆”的描述。"
  },
  {
    "question": "当锁升级为重量级锁时，对象头中的Mark Word存储了什么信息？",
    "options": [
      "持有锁的线程ID和锁的偏向状态。",
      "一个指向操作系统层面的Monitor对象的指针。",
      "对象的HashCode和GC分代年龄。",
      "一个指向线程栈中锁记录（Lock Record）的指针。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "进入重量级锁状态后，锁的管理完全委托给了操作系统。此时，对象头的Mark Word不再直接存储锁状态的详细信息，而是存储一个指针，该指针指向一个由操作系统内核管理的Monitor对象（也称为互斥锁）。这个Monitor对象内部包含了等待队列、所有者信息等，用于管理线程的阻塞和唤醒。",
    "source": "文档中「4. 重量级锁 (Heavyweight Locking)」部分",
    "hint": "重量级锁依赖于操作系统的能力，因此Mark Word需要一个“桥梁”来连接到操作系统的同步原语。"
  },
  {
    "question": "根据文档，以下哪项是避免不必要锁膨胀的有效策略？",
    "options": [
      "尽可能延长同步代码块的执行时间，以减少锁的获取次数。",
      "使用`Thread.sleep()`来强制线程等待，避免竞争。",
      "优化锁的粒度，例如缩小同步代码块的范围，从而降低锁的竞争。",
      "在程序启动时，通过JVM参数禁用偏向锁和轻量级锁。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "锁膨胀的根本原因是线程间的激烈竞争。通过优化代码，减小同步代码块的范围（即减小锁的粒度），可以显著缩短单个线程持有锁的时间，从而降低其他线程在同一时间点争抢该锁的概率。竞争减少了，锁膨胀为重量级锁的可能性自然也就降低了。",
    "source": "文档中「6. 如何避免锁膨胀」部分",
    "hint": "思考一下锁膨胀的根源是什么？文档中给出的建议是如何从源头上“降低锁的竞争”。"
  }
];
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                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  